1. Field of the Invention
This invention relates to a data system and more particularly to a data system that enables near video on demand transmission.
2. Description of the Prior Art
Near video on demand transmission (NVOD) is a multi-channel transmission technique that plays a motion-picture film (or other broadcast material) with fixed offset start times. If, for example, this offset start time was 8 minutes, then consumers would never have to wait longer than 8 minutes to see a film from the very beginning. This start time is commonly referred to in the art as "a spur".
NVOD is not in itself a new technology and various different apparatus have been manufactured to enable its implementation.
A typical prior art arrangement is to provide a RAID array of hard disks each of which has a high input bandwidth of around 250 Mbps (megabits per second). The RAID array is burst fed by video data from a high speed video data storage device. The RAID array then outputs its information to each channel at a much lower bandwidth (typically between 4 to 10 Mbps) for viewing. The RAID array typically has an input bandwidth some 25 times that of the final output bandwidth of each channel. This prior art arrangement is of a large physical size and is unduly expensive to manufacture. Much of that expense is incurred by providing a RAID array that, by necessity, has an input bandwidth that is much higher than the required output bandwidth.
An alternative apparatus that seeks to address some of these problems utilises magneto-optical (MO) storage systems to reduce the required input/output bandwidth. In one such example, an MO disk storage system feeds 16 decoders, each operating at around 4 megabits per second. In this example, the MO disk has an input bandwidth some 16 times that of the final output bandwidth and so, the input bandwidth has been reduced in comparison to that of the first example given above. However, in order to achieve this reduction in input bandwidth, an MO technology has to be used that requires all video data to be preformatted on an MO disk. Any subsequent changes, such as censoring, of the preformatted video data would require a repeat formatting of the MO disk with the new information. Thus, the new apparatus, whilst having a reduced input bandwidth, is now relatively inflexible as it requires a special formatting of the video data prior to its transmission.